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Elixir Cookbook

By : Paulo Pereira

4.5 (2)

Elixir Cookbook

4.5 (2)

By: Paulo Pereira

Overview of this book

This book is intended for users with some knowledge of the Elixir language syntax and basic data types/structures. Although this is a cookbook and no sequential reading is required, the book’s structure will allow less advanced users who follow it to be gradually exposed to some of Elixir’s features and concepts specific to functional programming. To get the most out of this book, you need to be well versed with Erlang.

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Sections

Conventions

Reader feedback

Customer support

Free Chapter

1. Command Line

1. Command Line

Introduction

Using the terminal to prototype and test ideas

Loading and compiling modules

Getting help and accessing documentation within IEx

Using Erlang from Elixir

Inspecting your system in IEx

Inspecting your system with Observer

Creating a simple application

Managing dependencies

Generating a supervised application

Generating umbrella applications

Managing application configuration

Creating custom Mix tasks

2. Data Types and Structures

2. Data Types and Structures

Understanding immutability

Adding and subtracting lists

Combining tuples into a list

Creating and manipulating keyword lists

Using pattern matching

Pattern matching an HTTPoison response

Creating a key/value store with a map

Mapping and reducing enumerables

Generating lazy (even infinite) sequences

Streaming a file as a resource

3. Strings and Binaries

3. Strings and Binaries

Introduction

Joining strings

Splitting strings

Replacing string codepoints with patterns

Slicing strings with ranges

Using regular expressions

Combining operations with the |> operator

Creating a word list

Determining the word frequency in a text

Reading and writing metadata from MP3 files

4. Modules and Functions

4. Modules and Functions

Introduction

Namespacing modules

Using module attributes as constants

Enforcing behaviors

Documenting modules

Using module directives

Using a module in the scripted mode

Defining functions with default arguments

Using guard clauses and pattern matching in function definitions

5. Processes and Nodes

5. Processes and Nodes

Introduction

Sending messages between processes

Making code run on all available CPUs

Using tasks to perform multiple concurrent computations

Creating a stateful server process (messages with counters)

Using agents as an abstraction around states

Using an ETS table to share the state

Creating named nodes

Connecting nodes

Executing code in a different node

6. OTP – Open Telecom Platform

6. OTP – Open Telecom Platform

Introduction

Implementing a GenServer

Expanding our server

Creating a supervisor

Using Observer to inspect supervisors and processes

Handling errors and managing exceptions

Packaging and releasing an OTP application

Deploying applications and updating a running system

7. Cowboy and Phoenix

7. Cowboy and Phoenix

Introduction

Setting up Cowboy

Serving static files

Implementing a websocket handler

Creating a Phoenix application

Defining routes

Creating a controller

Creating views and templates

Implementing topics

Protecting the Phoenix app with SSL

8. Interactions

8. Interactions

Introduction

Using Redis and Postgres

Using OS commands from within Elixir

Getting Twitter data

A. Installation and Further Reading

A. Installation and Further Reading

Installing Elixir

Installing PostgreSQL

Installing Redis

Some useful links

Index

Index

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Generating a supervised application

An application may be generated with a supervision tree to monitor processes. The supervision tree must be started and stopped with the application, and to do so, an application module callback must also be implemented. Mix provides a simple way to generate this type of application.

How to do it…

To generate an application with a supervision tree and an application module callback, we run mix new supervised_app –-sup in the command line. This is shown in the following screenshot:

How to do it…

How it works…

When mix new task is invoked with the –-sup option, although the generated application appears to be identical to the application created in the Creating a simple application recipe, a few things change, which are as follows:

supervised_app/mix.exs
def application do
  [applications: [:logger],
  mod: {SupervisedApp, []}]
end

An application module callback is added like this:

supervised_app/lib/supervised_app.ex
defmodule SupervisedApp do
  use Application
  def start(_type, _args) do
    import Supervisor.Spec, warn: false
    children = [
      # Define workers and child supervisors to be supervised
      # worker(SupervisedApp.Worker, [arg1, arg2, arg3])
    ]
    opts = [strategy: :one_for_one, name: SupervisedApp.Supervisor]
    Supervisor.start_link(children, opts)
  end
end

The Application module behavior is declared, and a start function must be defined to comply with this behavior. Inside the start function, a list of children (usually worker processes) is declared, and so are the supervision options (opts). The supervisor is then started, passing the list of processes to be supervised and the options.

See also

The documentation for the Application module can be accessed at http://elixir-lang.org/docs/stable/elixir/Application.html.
Information on the Supervisor module is available at http://elixir-lang.org/docs/stable/elixir/Supervisor.html.

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